It is known that the volt-ampere (V/I) characteristic of an electrical discharge, particularly for a fluorescent lamp, has a very low or even negative differential resistance, expressed as R.sub.d =dV/dI, which is much smaller than its static resistance, expressed as R.sub.s =V/I. This aspect of the discharge makes it necessary to employ a ballast to provide additional resistance for stable operation of the lamp from a source of voltage (source with a very low output resistance). For AC operation an inductive ballast is used for reducing ballast energy loss.
The nature of the low differential resistance of the discharge is that the plasma density and conductance of the discharge is nearly proportional to discharge current for slow changes of discharge current when plasma density is in equilibrium with the current. On the other hand, for fast current variation, for a time much less than the diffusion time T.sub.d (for fluorescent lamp T.sub.d is in the order of lms), the plasma density in nearly constant during a period of the AC signal. The instantaneous current-voltage characteristic of such a discharge is almost linear. Thus, by operating in this manner the differential resistance and static resistance are about equal. Thus, it is typical to provide high frequency lamp operation, say in a frequency range of 25-50 KHz. This is implemented by an electronic ballast which is essentially a high frequency signal generator with output power equal to the lamp discharge power. There are several drawbacks associated with a conventional high frequency electronic ballast including by way of example, their complexity and cost which follows from the requirement of total lamp power generation.